http://forums.debian.net/viewtopic.php?f=5&t=136156
Any suggestion appreciated.

https://askubuntu.com/questions/696676/grub-default-is-not-working-properly wrote:OK! I found the solution. I had to link a PPA to grub-customizer.
sudo add-apt-repository ppa:danielrichter2007/grub-customizer
Than I did:
sudo apt-get update
Next step is
sudo apt-get install grub-customizer
After that I open the grub-customizer through unity dash and select the desired kernel from there and tada!:)
I understand the concept and use it myself but maybe there is a bug in your system and it's tripping over it for some reason. It takes a sec to move it and see if it helps.
You're welcome.